The present invention relates to a control system for an internal combustion engine utilizing a variable compression ratio mechanism and boosting mechanism to improve engine performance.
Engines utilize various devices to improve fuel economy. For example, engines can include mechanisms for varying compression ratio and boosting devices for increasing manifold pressure.
In one example (U.S. Pat. No. 5,819,702), turbocharging is used and compression ratio is lowered at high power levels to prevent engine knock. Alternatively, no turbocharging is used and compression ratio is increased at low power levels. In another example (U.S. Pat. No. 5,845,613), an engine controller adjusts intake valve opening timing to prevent engine knock where the engine includes boosting.
The inventors herein have recognized a disadvantage with approaches that attempt to prevent engine knock using compression ratio. For example, using compression ratio to avoid knock can cause excessive hunting between various amounts of compression since varying compression ratio can affect engine breathing, which in turn also affects knock. This can lead to degraded drivability and increased emissions.
Further, the inventors herein have recognized that such approaches can create even further disadvantages. For example, when adjusting compression ratio, different ignition timing may be needed to provide peak efficiency. However, this adjustment in ignition timing may again lead to knock. Thus, compression ratio is further adjusted. Such an approach can thus actually lead to degraded efficiency and performance.
The above disadvantages are overcome by a system comprising an engine having a variable compression ratio mechanism and a controller. The controller indicates potential for engine knock; adjusts ignition timing in response to said indication when said engine is operating in a first region; and adjusts compression ratio of said compression ratio mechanism in response to said indication when said engine is operating in a second region.
By using different actuators to prevent engine knock in different regions, it is possible to minimize disadvantageous interaction between the actuators and thus provide improved engine performance.
In another aspect of the present invention, the controller adjusts ignition timing when engine ignition timing is retarded less than a first predetermined value and adjusts compression ratio of said compression ratio mechanism when engine ignition timing is retarded greater than a second predetermined value.
Thus, in one example according to the present invention, ignition timing can be used to prevent engine knock until the timing reaches a predetermined retard amount. Then, if there is still a potential for knock, compression ratio can be used. In this way, disadvantageous interaction between these two mechanisms is minimized and improved engine operation results.
In another aspect of the present invention, a boosting apparatus is coupled to the engine. Then, the controller adjusts compression ratio when ignition timing is retarded greater than a first predetermined value and adjusts said boosting apparatus when ignition timing is retarded greater than a second predetermined value and compression ratio of said variable compression ratio is less than a third predetermined value.
In this way, it is possible to coordinate the action of three devices, each of which can be controlled to prevent engine knocking.
Note that there are various types of compression ratio mechanisms as well as various types of boosting devices that can be used according to the present invention. For example, compression ratio can be adjusted by varying piston head height or connecting rod length, or any other such method. Further, boosting can be provided by turbocharging, turbocharging with intercooling, or supercharging.
Also note that there are various methods of specifying different operating regions. For example, these regions may be based on engine speed, engine airflow, ignition timing, engine torque, engine temperature, or various other parameters, as described later herein. Finally, note that there are various ways to adjust parameters, including increasing, decreasing, gradually changing, abruptly stepping, engaging, or discontinuing.